A process for the synthesis of polynorbornene or “poly(bicyclo[2.2.1]hept-2-ene)” or polyNB for brevity is reported in U.S. Pat. No. 2,721,189. However this original material was found to contain two types of polymers, one brittle, the other thermoformable and “drawable”. The brittle polymer was later found to be a low molecular weight saturated polymer which was termed an addition type polymer; and, the thermoformable polymer was shown to be formed by ring opening metathesis polymerization (ROMP). A ROMP polymer has a different structure compared with that of the addition polymer in that (i) the ROMP polymer of one or more NB-functional monomers, contains a repeat unit with one less cyclic unit than did the starting monomer, and, (ii) these are linked together in an unsaturated backbone characteristic of a ROMP polymer and is shown below.

Despite being formed from the same monomer, an addition-polymerized polyNB is clearly distinguishable over the polymer made by ROMP polymerization. Because of the different (addition) mechanism, the repeating unit of the former has no backbone carbon-carbon double bond unsaturation as shown below:

The difference in structures of ROMP and addition polymers of NB-functional monomers is evidenced in their properties, e.g., thermal properties. The addition type polymer of NB has a high glass transition temperature (Tg) of about 370° C. The unsaturated ROMP polymer of NB exhibits a Tg of about 35° C., and exhibits poor thermal stability at high temperature above 200° C. because of its high degree of carbon-carbon unsaturation.
Over the years, reaction conditions have been optimized so as to enable one to choose, and selectively make, either the low molecular weigh addition polymer, or the ROMP polymer. For instance, U.S. Pat. No. 3,330,815 indicates that only the addition polymer is synthesized with TiCl4/Et2AlCl or Pd(C6H5CN)2Cl2, under particular conditions, except that the polymers produced are only those in the molecular weight range from 500 to 750 in which range they are too brittle for any practical application.
Addition polymers of norbornene have been shown to be produced with “zirconocene type” catalysts such as those taught by Kaminsky et al. These polymers have been found to be a highly crystalline form of a “norbornene-addition polymer”, that is, an addition polymer of a NB-functional monomer, which is totally insoluble, and reportedly does not melt until it decomposes at about 600° C. (under vacuum to avoid oxidation). It is therefore unprocessable (W. Kaminsky et al., J. Mol. Cat. 74, (1992), 109; W. Kaminsky et. al. Makromol. Chem, Macromol. Symp., 47, (1991) 83; and W. Kaminsky, Shokubai, 33, (1991) 536.). An added distinguishing characteristic of the zirconocene catalyst system is that it catalyzes the copolymerization of ethylene and norbornene. In such copolymers, the amount of NB incorporated into the ethylene/NB copolymer can be varied from high to low (W. Kaminsky et. al. Polym. Bull., 1993, 31, 175).
The polymer formed with a zirconocene catalyst can incorporate ethylene (or compounds containing ethylenic unsaturation at a terminal end thereof) in its backbone, randomly, whether in runs of a multiplicity of repeating units, or even a single unit. It should also be noted that the ionic metallocene catalysts, such as zirconocenes and hafnocenes, use metals from Group IVB as the cation with a compatible weakly coordinating anion.
Research has continued toward the production of a melt-processable addition polymer of a NB-type monomer, and is the subject of an on-going effort. By “melt-processable” it is meant that the polymer is adequately flowable to be thermoformed in a temperature window above its glass transition temperature (Tg) but below its decomposition temperature. Norbornene monomer, bicyclo[2.2.1]hept-2-ene or “NB” for brevity, and substituted embodiments thereof, such as ethylidenenorbornene or decylnorbornene, and particularly those monomers of NB having at least one substituent in the 5-(and/or 6-) positions are commonly referred to as “norbornene-functional monomers.” The foregoing monomers are characterized by containing a repeating unit resulting from an addition polymerized derivative of bicyclo[2.2.1]hept-2-ene. A first NB-functional monomer may be polymerized by coordination polymerization to form (i) an addition homopolymer; or, (ii) with a second NB-functional monomer, either one (first or second) of which is present in a major molar proportion relative to the other, to form an addition NB-functional copolymer; or, (iii) with a second monomer which is not an NB-functional monomer, present in a minor molar proportion relative to the first, to form an addition copolymer with plural repeating units of at least one NB-functional monomer.
A few years ago the reactivity of cationic, weakly ligated, transition metal compounds was studied in the polymerization of olefins and strained ring compounds, (A. Sen, T. Lai and R. Thomas, J. of Organometal. Chemistry 358 (1988) 567–568, C. Mehler and W. Risse, Makromol. Chem., Rapid Commun. 12, 255–259 (1991)). Pd complexes incorporating the weakly ligating CH3CN (acetonitrile) ligand in combination with a weakly coordinating counteranion could only be used with aggressive solvents such as acetonitrile or nitromethane. When Sen et al used the complexes to polymerize NB, a high yield of a homopolymer which was insoluble in CHCl3, CH2Cl2 and C6H6, was obtained.
The identical experimental procedure, with the same catalyst and reactants, when practiced by Risse et al used one-half the molar amount of each component. Risse et al reported the synthesis of a poly-NB homopolymer which had a number average molecular weight (Mn) of 24,000. In other runs, using different ratios of NB to Pd2+ compound, poly-NBs having number average molecular weights of 38,000 and 70,000 respectively with narrow polydispersities Mw/Mn in the range from 1.36 to 1.45, and viscosities in the range from 0.22 to 0.45 dL/g were made. A homopolymer which had a viscosity of 1.1 was synthesized, which upon extrapolation from the molecular weight data given for the prior runs, indicates the weight average molecular weight (Mw) was over 1,000,000. See Mehler and Risse Makromol. Chem., Rapid Commun. 12, 255–9 (1991), experimental section at the bottom of page 258 and the GPC data in Table 1 on page 256. The polymers were soluble in 1,2-dichlorobenzene in which Risse et. al. measured molecular weights by GPC (gel permeation chromatography) and viscometry, as did Maezawa et al in EP 445,755A, discussed below.
Maezawa et al disclosed the production of high molecular weight NB polymers with a two-component catalyst system. The disclosure states that the polymer is preferably formed in the molecular weight range from 100,000 to 10,000,000. The manner of obtaining the desired molecular weight is shown to be by terminating the polymerization reaction after a predetermined period. Such termination is effected by decomposing the catalyst with an external terminating agent such as acidified methanol, which is added to the reaction to stop the polymerization. There is no internal control of the molecular weight within a predetermined range by an agent that does not deactivate the catalyst.
Specifically, three known methods of controlling the molecular weight are suggested: (i) varying the amount of the transition metal compound used; (ii) varying the polymerization temperature; and (iii) using hydrogen as a chain transfer agent “CTA” (see page 9, lines 20–23 of the EP 445,755A disclosure) as suggested by Schnecko, Caspary and Degler in “Copolymers of Ethylene with Bicyclic Dienes” Die Angewandte Makromolekulare Chemic, 20 (1971) 141–152 (Nr.283). Despite the foregoing suggestions, there is no indication in EP 445,755A that any of them was effective, as is readily concluded from the illustrative examples in the specification. As stated in their illustrative Example 1 in which the catalyst included a combination of nickel bisacetylacetonate Ni(acac)2 and methaluminoxane (“MAO”), a polyNB having Mw of 2.22×106 (by GPC) was formed. As shown in Table 1 of EP 445,755A, only Examples 5, 6 and 7, in which the (triphenylphosphine)Ni-containing catalysts were used, made homopolymers with weight average moleculoar weights of 34,000; 646,000; and 577,000 respectively. These nickel catalysts with a triphenylphosphine ligand, are shown to have relatively lower productivity than the biscyclooctadienylnickel (see Example 3) and biscyclopentadienylnickel (Exzmple 4) which were also used.
Allylnickelhalides alone (no Lewis acid cocatalyst) have been used to produce polyNB. The molecular weights of the NB polymer produced in these studies were within the range of 1000 to 1500 (L. Porri, G. Natta, M. C. Gallazzi Chim. Ind. (Milan), 46 (1964), 428). It had been thought that the low yields and the low molecular weights of the polyNB were due to deactivation of the catalysts.
EP 504,418A discloses the use of a nickel catalyst as a transition metal equivalent to zirconium for the production of high molecular weight norbornene polymer with a three component catalyst system (see Example 117). The three-component catalyst was made in situ by combining triisobutylaluminum; dimethylanilinium tetrakis(pentafluorophenyl)borate; and, Ni(acac)2 in toluene. The polymer recovered had a weight average molecular weight (Mw) of 1.21×106 and a polydispersity of 2.37. Though essentially the entire specification is directed to the copolymerization of cycloolefins with α-olefins using zirconium-containing catalysts, Okamoto et al did not react norbornene and α-olefin with a nickel catalyst. Nowhere in the EP 504,418A specification is there a teaching that the use of an α-olefinic CTA will control molecular weight. There is no teaching of a polymer with a terminal olefinic end-group. Nor is there any teaching that an α-olefin would do anything but copolymerize.
The failure to recognize that an a-olefin might function as a CTA, with or without the presence of an alkylaluminum cocatalyst, was understandable since there existed a large body of work related to the copolymerization of cycloolefins with α-olefins, and in none of such polymerizations was there any disclosure that the α-olefin might function as an effective CTA. Further, the great reactivity of ethylene or propylene buttressed an expectation that copolymerization, not chain transfer, is the logical and expected result.
Acyclic olefins, such as 1-hexene, are known to be effective for utilization as a CTA in the ROMP of cyclic olefins, to reduce molecular weight via a cross-metathesis mechanism. ROMP involves a metal carbene (or metal alkylidene) active center which interacts with the cyclic olefin monomer to afford a metallocycloalkane intermediate. A repeating unit contains a carbon-carbon double bond (—C═C—) for every carbon-carbon double bond in the monomer. How effectively the acyclic olefin reduces the molecular weight of the copolymer formed depends on the structure of the olefin and on the catalyst system (K. J. Ivin, Olefin Metathesis, Academic Press, 1983). In contrast, addition (or vinyl type) polymerization of olefins and diolefins involves the insertion of the monomer into a metal-carbon a-bond, as in Ni—C, or Pd—C. Despite the many disclosures relating to the formation of copolymers of NB-type monomers, and the well-known fact that an olefin is an effective chain transfer agent in a ROMP polymerization, it will now be evident why the difference in the mechanisms of chain termination failed to suggest the use of an olefin as a chain transfer agent in the copolymerization taught herein.
U.S. Pat. No. 5,571,881 discloses addition polymers derived from norbornene-functional monomers that are terminated with an olefinic moiety derived from a chain transfer agent selected from a compound having a terminal olefinic double bond between adjacent carbon atoms, excluding styrenes, vinyl ethers, and conjugated dienes wherein at least one of said carbon atoms has two hydrogen atoms attached thereto. The addition polymers of described in this patent are prepared from a single or multicomponent catalyst system including a Group VIII metal ion source. These catalyst systems are unique in that they catalyze the insertion of the chain transfer agent exclusively at a terminal end of the polymer chain. U.S. Pat. No. 5,571,881 more specifically discloses a process for controlling the molecular weight of an addition polymer comprising repeating units polymerized from one or more norbornene-functional monomers, said process comprising reacting a reaction mixture comprising at least one norbornene-functional monomer, a solvent for said monomer and an effective amount of a single or multicomponent catalyst system each comprising a Group VIII transition metal source and a chain transfer agent selected from a compound having a terminal olefinic double bond between adjacent carbon atoms, excluding styrenes, vinyl ethers, and conjugated dienes, and at least one of said adjacent carbon atoms has two hydrogen atoms attached thereto.